Experiments on 24-h cycles of sensory performance are proposed, with an emphasis on free-running rhythms under constant environmental conditions, and entrainment patterns in the presence of daily periodic cues. The data will extend previous analyses of general behavioral activity rhyttms to psychophysical detection behavior under the control of weakly discriminable stimuli. Circadiaan periodicity in the discriminability of visual and auditory stimuli will be the focus of attention, and food-entrainment schedules will be investigated as a means to control the period and phase of sensory oscillations in the absence of light-dark Zeitgebern. The effect of lesions of the hypothalamic suprachiasmatic nucleus will be studied to assess possible differential control mechanisms in circadian motor activity and sensory functions.